1. Field of the Invention
The present invention relates to an image sensor and an optical character reader and particularly to an improved image sensor usable in optical character readers.
2. Description of the Related Art
An image sensor comprises an array of light emitting elements such as LED""s or the like, from which light is irradiated on an original document within a given range of lines. The light reflected by the original document is then condensed by a condensing lens, the condensed light being received by an array of light receiving elements wherein the light is converted into an electrical signal including image information for the original document. Such a reading cycle for each line is repeated to read the overall information of the original document image. Such an image sensor is known as a xe2x80x9cline image sensorxe2x80x9d and is frequently used in the image reading section of an optical character reader such as a facsimile machine.
FIG. 5 shows an image sensor 130 which is generally used in the optical character reader. The image sensor 130 comprises a frame 110, the top of which supports a transparent covering (glass covering) 111. Within the interior of the frame 110, there are disposed a light emitting element 112 for irradiating light onto an original document W placed on the transparent covering 111; a base plate 113 on which the light emitting element 112 is mounted; a rod lens array 114 which is normally used as an optical system for condensing the light reflected by the original document W; a light receiving element 115 for receiving the light from the rod lens array 114; and another base plate 116 on which the light receiving element 115 is mounted.
In such an image sensor 130 of the related art, the original document W, which is being moved by a platen roller 120, is irradiated by the light from the light emitting element 112 at the same time as the original document W is brought into contact with the transparent covering 111. The angle of irradiation between the transparent covering 111 and the light beam from the light emitting element 112 is equal to about 45 degrees. The light reflected from the original document W is therefore received and condensed by the rod lens array 114 which is located at a position perpendicular to the surface of the transparent covering 111. After passing through the rod lens array 114, the light is received by the light receiving element 115 which is positioned directly below the rod lens array 114 and which converts the light into the electrical signal.
If an optical path from the original document W to the light receiving element 115, that is, a focal length H from the top of the transparent covering 111 to the light receiving element 115 is not correct, the reflected light will be out of focus, resulting in improper detection of the light information of the original document W at the light receiving element 115.
In the aforementioned image sensor, however, the transparent covering 111, rod lens array 114 and light receiving element 115 are fixedly mounted in the optical path within the exterior of the frame 110. This raises a problem in that the focal length H may be varied depending on the dimensional accuracy in the frame 110. Particularly, if the dimensional accuracy of the frame 110 is very low, the focal length H will be greatly varied. This will undoubtedly lead to the light being out of focus.
In order to overcome such a problem, an image sensor has been proposed which can regulate the focus by controllably moving the rod lens array 114 in the vertical direction. In the proposed image sensor, the rod lens array 114 is mounted on the frame 110 by screw means. When the screw means is suitably tightened or untightened, the position of the rod lens array 114 can be adjusted.
However, such an adjustment is troublesome. Furthermore, threaded apertures for receiving the screws must be formed in both the frame and rod lens array 110, 114. This results in increase of the manufacturing cost.
It is therefore an object of the present invention to provide an image sensor which can be have its focus easily adjusted even if the dimensional accuracy in the frame is low and which comprises an inexpensive focus adjusting means for attaining the aforementioned adjustment.
Another object of the present invention is to provide an optical character reader which uses the abovementioned image sensor.
To this end, the present invention provides an image sensor comprising a frame having an opened top; a transparent covering mounted over the opened top of the frame and adapted to receive an original document to be read; a platen roller for moving the original document onto the transparent covering; a light emitting section for irradiating light onto the original document; an optical system for condensing the light reflected by the original document; and a light receiving section for receiving the condensed light through the optical system, the opened top of the frame having inner tapered sidewalls opposed to each other, whereby the focal length from the transparent covering to the light receiving section can be adjusted by mounting the transparent covering in the opened top of the frame while adjusting the angle of the transparent covering relative to the inner tapered sidewalls of the frame.
The present invention also provides an image sensor comprising a frame having an opened top; a transparent covering mounted over the opened top of the frame and adapted to receive an original document to be read; a platen roller for moving the original document onto the transparent covering; a light emitting section for irradiating light onto the original document; an optical system for condensing the light reflected by the original document; and a light receiving section for receiving the condensed light through the optical system, the opened top of the frame having inner tapered sidewalls opposed to each other, the transparent covering including top and bottom chamfered edges having different angles, whereby the focal length from the transparent covering to the light receiving section can be adjusted by selecting and using either of the top or bottom chamfered edge when the transparent covering is to be mounted in the opened top of the frame.
The present invention further provides an optical character reader comprising an original document supply section including a feed-in tray for retaining a stack of original documents to be read, a feed roller for picking up and conveying the uppermost original document from the stack and an image sensor for reading characters on the original document conveyed by the feed roller as image signals; a recording sheet supply section including a platen roller for conveying a recording sheet to which the characters on the original document are to be transferred; and a thermal transfer printing section for printing the image read by the image sensor on the recording sheet, the image sensor comprising a frame having an opened top; a transparent covering mounted over the opened top of the frame and adapted to receive an original document to be read; a platen roller for moving the original document onto the transparent covering; a light emitting section for irradiating light onto the original document; an optical system for condensing the light reflected by the original document; and a light receiving section for receiving the condensed light through the optical system, the opened top of the frame having inner tapered sidewalls opposed to each other, whereby the focal length from the transparent covering to the light receiving section can be adjusted by mounting the transparent covering in the opened top of the frame while adjusting the angle of the transparent covering relative to the inner tapered sidewalls of the frame.
The present invention further provides an optical character reader comprising an original document supply section including a feed-in tray for retaining a stack of original documents to be read, a feed roller for picking up and conveying the uppermost original document from the stack and an image sensor for reading characters on the original document conveyed by the feed roller as image signals; a recording sheet supply section including a platen roller for conveying a recording sheet to which the characters on the original document are to be transferred; and a thermal transfer printing section for printing the image read by the image sensor on the recording sheet, the image sensor comprising a frame having an opened top; a transparent covering mounted over the opened top of the frame and adapted to receive an original document to be read; a platen roller for moving the original document onto the transparent covering; a light emitting section for irradiating light onto the original document; an optical system for condensing the light reflected by the original document; and a light receiving section for receiving the condensed light through the optical system, the opened top of the frame having inner tapered sidewalls opposed to each other, the transparent covering including top and bottom chamfered edges having different angles, whereby the focal length from the transparent covering to the light receiving section can be adjusted by selecting and using either of the top or bottom chamfered edge when the transparent covering is to be mounted in the opened top of the frame.
In the image sensor and optical character reader of the present invention, the inner tapered sidewalls of the opened top of the image sensor frame enable the transparent covering to be mounted in the opened top of the frame while adjusting the angle of the transparent covering relative to the inner tapered sidewalls of the frame. Therefore, if the dimensional accuracy of the image sensor frame is very low, the focal length from the top face of the transparent covering to the light receiving section can be easily adjusted.
Since the opened top of the image sensor frame has the inner tapered sidewalls and also the transparent covering includes top and bottom chamfered edges having different angles, the focal length from the transparent covering to the light receiving section can be easily adjusted by selecting and using either of the top or bottom chamfered edge when the transparent covering is to be mounted in the opened top of the frame.